2. Electricity
HISTORICAL :
6th Century B.C., Greeks noticed sparks were produced when the
fossilized tree resin
called AMBER was rubbed with fur.
AMBER – comes from the Greek word ELEKTRON from which the word
electricity is derived.
End of 19th and early 20th Century:
Fundamental discoveries concerning the electronic structure of the atom
were made.
3. Important uses of Electricity
Light
Heat
Rail travel
Computers
Central nervous system
Medical/ Dental
9. Atoms are electrically neutral
total positive charge of the nucleus = total negative
charge of the electrons around the nucleus
These particles:
Neither created nor destroyed
Electrons can be displaced from one atom to another
Electron removed – result –positive ion
Electron added – result – negative ion
10. Electric charge
Basic physical property of subatomic particles.
3 characteristics of charge:
1. two types of charges: positive and negative
2. charge is conserved
3. like charges repel and unlike charges attract
12. The world is filled with electrical charges:
+
-
+
+
+ +
+
+
-
-
-
-
-
-
13. Basic unit of positive charge: +e = 1.6 x
𝟏𝟎−𝟏𝟗 Coulomb
Basic unit of negative charge: -e = -1.6
x 𝟏𝟎−𝟏𝟗 Coulomb (C)
14. Almost any two non-conducting substances
when rubbed together will become charged
plastic comb run through your hair,
comb will then attract bits of paper
Balloon and wool rubbed together:
balloon becomes negatively charged
15.
16. Friction associated with rubbing does not
create the charge
Charge transferred by movement of
electrons
Charge is conserved; neither created or
destroyed
Total amount of charge in universe:
constant
17. Coulomb’s Law
Charles Coulomb (1736-1806)
French physicist
‘’ the force between two point charges is
proportional to the product of their charge and
inversely proportional to the square of their
separation’’
Direction of the force: along line joining the point
charges
18. F ∝
𝑞1𝑞2
𝑟2 F= k
𝑞1𝑞2
𝑟2
Force F is known as the Coulomb force or electrostatic force
and its units are Newtons
Distance r is in meters
K - N𝑚2
𝐶−2
The constant k is determined by experiment to be 9 x
109
N𝑚2
𝐶−2
(in a vacuum)
k =
1
4𝜋𝜀0
19. Where 𝜀0 is called the permittivity of
vacuum
𝜀0 = 8.85 x 10−12
𝐶2
𝑁−1
𝑚−2
F = (
1
4𝜋𝜀0
)
𝑞1𝑞2
𝑟2
20. Example:
Two charges, each of one Coulomb, are a distance of 1 meter apart. What is the
force between them?
Given:
1 Coulomb (2)
r- 1 meter
F= N
F=
𝟏
𝒓𝝅𝜺𝟎
𝒒𝟏𝒒𝟐
𝒓𝟐 =
𝟏𝑪 ∗𝟏𝑪
𝟒𝝅𝟖.𝟖𝟓 𝒙 𝟏𝟎−𝟏𝟐𝑪𝟐𝑵−𝟏𝒎−𝟐∗𝟏𝒎∗𝟏𝒎
F= 9x𝟏𝟎𝟗
N = 9 billion Newtons
21. Electrostatic Force and Gravitational force can both act
through space even when there is no physical contact
between the objects involved.
Gravitational field = g
Mass m experiences a force
F = mg
PE≈ 𝒎𝒈𝒉
An electric field exists in a region of space around
a charged object.
22. Electric field near a negative charge is directed radially into the
charge.
Electric field near a positive charge is directed radially out from
the charge.
Double the charge, double the number of field lines
Electric field lines show :
Direction of the force
Indicate its relative magnitude
23. Electric field is said to exist in the region
of space around a charged object
TEST CHARGE
Q 𝒒𝟎
24. Force F experienced by test charge 𝑞0at a
given location.
Electric field E due to charge Q at location
of small test charge 𝒒𝟎 is given by:
E=
𝒇
𝒒𝟎
SI unit of electric field – Newtons per
Coulomb (N𝑪−𝟏
)
25. What is this electrical potential called?
What is this electrical potential called?
26. STATIC ELECTRICITY
The build up of an electric charge on
the surface of an object.
The charge builds up but does not
flow.
Static electricity is potential energy. It
does not move. It is stored.
27. STATIC DISCHARGE
Occurs when there is a loss of static electricity
due to three possible things:
◦Friction - rubbing
◦Conduction – direct contact
◦Induction – through an electrical field (not direct
contact)
32. What is the difference between static electricity and
current electricity?
Static electricity is stationary or collects on the surface of an
object, whereas current electricity is flowing very rapidly
through a conductor.
The flow of electricity in current electricity has electrical
pressure or voltage. Electric charges flow from an area of
high voltage to an area of low voltage.
35. The pressure of the water flowing through
the pipes on the last slide compare to the
voltage (electric potential) flowing through
the wires of the circuit. The unit used to
measure voltage is volts (V).
The flow of charges in a circuit is called
current. Current (I) is measured in Amperes
(A).
36. Circuits
Composed of individual electronic component such as
resistors, transistors, inductors, diodes, connected by
conductive wires or traces through which electric current
can flow.
CATEGORIES:
1. ANALOG CIRCUITS
2. DIGITAL CIRCUITS
3. MIXED SIGNAL CIRCUITS
37. There are 2 types of circuits:
Series Circuit: the components
are lined up along one path. If
the circuit is broken, all
components turn off.
39. Parallel circuits
Parallel Circuit – there are several
branching paths to the components. If
the circuit is broken at any one branch,
only the components on that branch
will turn off.
40.
41.
42. What is the difference between an opencircuit and a
closedcircuit?
A closedcircuit is one in which the pathway of the electrical current is
complete and unbroken.
An opencircuit is one in which the pathway of the electrical current is
broken. A switch is a device in the circuit in which the circuit can be
closed (turned on) or open (turned off).
43. How is household wiring arranged?
Most household wiring is logically designed with a combination of
parallel circuits. Electrical energy enters the home usually at a
breaker box or fuse box and distributes the electricity through
multiple circuits. A breaker box or fuse box is a safety feature which
will open
44.
45. What are batteries?
Batteries are composed of a chemical substance which can generate voltage which can be used in a circuit.
There are two kinds of batteries: dry cell and wet cell batteries. Below is an example of a dry cell.
The zinc container of the
dry cell contains a moist
chemical paste surrounding
a carbon rod suspended in
the middle.
46. Wetcell batteries are most commonly associated with automobile
batteries.
A wet cell contains two connected plates
made of different metals or metal
compounds in a conducting solution.
Most car batteries have a series of six
cells, each containing lead and lead
oxide in a sulfuric acid solution.
47. Conductors vs. Insulators
Conductors – material through which
electric current flows easily.
Insulators – materials through which
electric current cannot move.
49. What is Resistance?
The opposition to the flow of an electric
current, producing heat.
The greater the resistance, the less current
gets through.
Good conductors have low resistance.
Measured in ohms.
50. The metal which makes up a light
bulb filament or stovetop eye has a
high electrical resistance. This causes
light and heat to be given off.
51.
52. What Influences Resistance?
Material of wire – aluminum and copper have
low resistance
Thickness – the thicker the wire the lower the
resistance
Length – shorter wire has lower resistance
Temperature – lower temperature has lower
resistance
53. What is Voltage?
The measure of energy given to the
charge flowing in a circuit.
The greater the voltage, the greater the
force or “pressure” that drives the
charge through the circuit.
55. Difference b/t Volts and Amps
Example – you could say that…
◦Amps measure how much water comes out of a
hose.
◦Volts measure how hard the water comes out of a
hose.
56. How is Electrical Power calculated?
Electrical Power is the product of the current (I) and the voltage
(v)
The unit for electrical power is the same as that for mechanical
power in the previous module – the watt (W)
57. Example Problem: How much power is used
in a circuit which is 110 volts and has a
current of 1.36 amps?
P = I V
Power = (1.36 amps) (110 V) = 150 W
58. How is electrical energy determined?
Electrical energy is a measure of the amount of
power used and the time of use.
Electrical energy is the product of the power and
the time.
59. E = P X time
P = I V
P = (2A) (120 V) = 240 W
E = (240 W) (4 h) = 960Wh = 0.96 kWh
63. • Resistors are used for:
– Limiting current in electric circuits.
– Lowering voltage levels in electric circuits (using voltage divider).
– As current provider.
– As a sensor (e.g., photo resistor detects light condition, thermistor
detects temperature condition, strain gauge detects load condition,
etc.)
– In electronic circuits, resistors are used as pull-up and pull-down
elements to avoid floating signal levels.
65. Resistor Labels
• Wire-wound resistors have a label indicating resistance and power ratings.
• A majority of resistors have color bars to indicate their resistance
magnitude.
• There are usually 4 to 6 bands of color on a resistor. As shown in the figure
below, the right most color bar indicates the resistor reliability, however,
some
resistor use this bar to indicate the tolerance. The color bar immediately left
to
the tolerance bar (C), indicates the multipliers (in tens). To the left of the
multiplier bar are the digits, starting from the last digit to the first digit.
67. Resistor Color Codes
Color Tolerance
Brown ±1%
Red ±2%
Gold ±5%
Silver ±10%
None ±20%
Band color Digit Multiplier
Black 0 X1
Brown 1 X10
Red 2 X100
Orange 3 X1000
Yellow 4 X10000
Green 5 X100000
Blue 6 X1000000
Purple 7 X10000000
Grey 8 X100000000
White 9 X1000000000
Silver - x.01
Gold - x.1
68. The first band is yellow, so the first digit is 4
• The second band is violet, so the second digit is 7
• The third band is red, so the multiplier is
• Resistor value is 47 x 102
± 5% (Ω)
69. Digital Multimeter
DMM is a measuring instrument
• An ammeter measures current
• A voltmeter measures the potential
difference (voltage) between two
points
• An ohmmeter measures resistance
• A multimeter combines these
functions, and possibly some
additional ones as well, into a single
instrument
70. • Voltmeter
– Parallel connection
• Ammeter
– Series connection
• Ohmmeter
– Without any power supplied
• Adjust range (start from highest
limit if you don’t know)
71. Resistance Formula
for a resistor made using a homogenous material
R=
𝝆𝑳
𝑨
WHERE:
𝝆 = specific resistance of material (material property)
L = length of conductor used to make the resistor
A = cross-section area of conductor used to make the
resistor
72. A capacitor is an energy storage element which is analogous to the
spring element of mechanical systems.
•It can store electrical pressure (voltage) for periods of time.
-When a capacitor has a difference in voltage (electrical
pressure) across its plate, it is said to be charged.
-A capacitor is charged by having a one-way current flow
through it for a period of time.
-It can be discharged by letting a current flow in the opposite
direction out of the capacitor.
73. Capacitor construction
A capacitor is constructed using a pair of
parallel conducting plates separated by an
insulating material (dielectric)
When the two plates of a capacitor are
connected to a voltage source as shown,
charges are displaced from one side of the
capacitor to the other side, thereby
establishing an electric field.
The charges continue to be displaced in this
manner until the potential difference across
the two plates is equal to the potential of the
voltage source.
74. Capacitor V-I characteristics
The charge accumulated on capacitor plates is directly proportional to voltage applied
across the plates.
q ∝ 𝑽 →q = CV
WHERE C is constant of proportionality and is called capacitance (unit: Farad)
V-I characteristic of a capacitor is obtained by computing
𝒅
𝒅𝒕
[𝒒 = 𝑪𝑽] →
𝒅𝒒
𝒅𝒕
= c
𝒅𝒗
𝒅𝒕
→ 𝑰 𝒕 = 𝒄
𝒅𝒗
𝒅𝒕
Alternatively, integrating the above equation w.r.t. time, and rearranging terms, we geT
V(t)=
𝟏
𝑪 𝟎
𝒕
𝑰 𝝉 𝒅𝝉
75. Capacitance formula
For a parallel capacitor:
C=
𝜺𝟎𝑨
𝑫
Where:
𝜺 𝟎=𝒑𝒆𝒓𝒎𝒊𝒕𝒕𝒊𝒗𝒊𝒕𝒚 𝒐𝒇 𝒇𝒓𝒆𝒆 𝒔𝒑𝒂𝒄𝒆
𝑨=𝒑𝒍𝒂𝒕𝒆 𝒂𝒓𝒆𝒂
𝑫=𝒔𝒆𝒑𝒂𝒓𝒂𝒕𝒊𝒐𝒏 𝒅𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝒐𝒇 𝒑𝒍𝒂𝒄𝒆
76. •Electrolytic
–Aluminum, tantalum electrolytic
–Tantalum electrolytic capacitor has a
larger capacitance when compared to
aluminum electrolytic capacitor
–Mostly polarized.
–Greater capacitance but poor tolerance
when compared to nonelectrolytic
capacitors.
–Bad temperature stability, high
leakage, short lives
•Ceramic capacitors
–very popular nonpolarized
capacitor
–small, inexpensive, but poor
temperature stability and poor
accuracy
–ceramic dielectric and a phenolic
coating
–often used for bypass and
coupling
applications
77. CAPACITOR VARIATION
•Mica
–extremely accurate, low leakage
current
–constructed with alternate layers of
metal foil and mica insulation,
stacked and encapsulated
–small capacitance
–often used in high-frequency
circuits (i.e. RF circuits)
•Mylar
–very popular, nonpolarized
–reliable, inexpensive, low
leakage
–poor temperature stability
80. INDUCTOR
Inductor is a passive energy storage element that stores energy in the form of
magnetic field.
•Inductor characteristic is governed by
Faraday’s law:
V(t)=
𝒅𝝀
𝒅𝒕
–V = voltage induced across an inductor
–𝝀 = magnetic flux (unit: Webers, Wb) through the coil windings (a coil made
using resistance-less wires) due to current flowing through inductor.
V(t)=
𝑑λ
𝑑𝑡
83. •Tuning coil
–screw-like “magnetic field
blocker” that can be adjusted to
select the desired inductance
value
–used in radio receivers to select
a desired frequency.
85. •Toroidal coil
–resembles a donut with a
wire wrapping
–high inductance per
volume ratios, high quality
factors, self-shielding, can
be operated at extremely
high frequencies
86. Transformers
•Isolation
–acts exclusively as an isolation
device; does not increase or
decrease the secondary voltage
–usually come with an electrostatic
shield
between the primary and secondary.
Often come with a three-wire plug
and receptacle that can be plugged
directly into a power outlet
87. •High Frequency
–often come with air or
powered-iron cores
–used for high frequency
applications, i.e. matching
RF
transmission lines to
other devices
(transmission line to
antenna)
•Audio
–used primarily to match
impedances between audio
devices
–work best at audio frequencies
from 150Hz to 12kHz
–come in a variety of shapes and
sizes, typically contain a center
tap
89. Historical
First magnets were pieces of lodestone (magnetite, 𝑭𝒆𝟑𝑶𝟒)
found originally in Asia (magnesia)
Materials :
Iron is one of a few materials (also Nickel, Cobalt) that can
be permanently magnetised
These are called FERROMAGNETIC MATERIALS
90. Lodestone
• Lodestones attracted iron
filings.
• Lodestones seemed to
attract each other.
• Used as a compass.
– One end always pointed
north.
• Lodestone is a natural
magnet.
92. Applications
• Motors
• Navigation – Compass
• Magnetic Tapes
– Music, Data
• Television
– Beam deflection Coil
• Magnetic Resonance Imaging
• High Energy Physics Research
93. Permanent Vs. Temporary
Magnets can be permanent or temporary.
A magnet is permanent when the material inside
always produces a magnetic field.
Example: a bar magnet
94. A magnet is temporary when the material inside only
produces a magnetic field when electric current is
passed through it.
Example: an electromagnet
95. When a current passes through a simple wire, a magnetic field is created around the
wire, this is due to the flow of the electrons.
96. The microscopic origin of the magnetism
in magnets
ORBITING ELECTRONS
oELECTRONS are moving around the nucleus,
electrons orbiting constitute a circular
current loop, so each electron generates a
tiny magnetic field.
97. SPINNING ELECTRONS
oELECTRONS also act as though they are
spinning about an axis through their
centres.
oSpinning electron also act like a current
loop and so creates a tiny magnetic
field.
102. The earth is like a giant magnet!
The nickel iron core of the earth gives the earth a magnetic field much
like a bar magnet.
103. Observations
• Bring a magnet to a charged electroscope and nothing happens. No
forces.
• Bring a magnet near some metals (Co, Fe, Ni …) and it will be
attracted to the magnet.
– The metal will be attracted to both the N and S poles independently.
– Some metals are not attracted at all.
– Wood is NOT attracted to a magnet.
– Neither is water.
• A magnet will force a compass needle to align with it. (No big
Surprise.)
+
+
+
104. An electromagnet is a temporary magnet created by
coiling a wire around a metal core, and passing a
current through the wire.
105. Characteristics of electromagnets
Magnetic field
The magnetic field around an electromagnet is
just the same as the one around a bar magnet.
Unlike bar magnets, which are permanent
magnets, the magnetism of electromagnets
can be turned on and off just by closing or
opening the switch.
106. Magnetic Poles
They still have a north and a south pole.
When the direction of the electric current is
switched, poles can change places.
107. Magnetic Attraction
Attracts other magnetic materials.
When current is turned on, the magnet
may be attracted to (or repelled by) other
magnets.
108. The type of core (metal the coil is wrapped
around)
Iron cores create the strongest electromagnets.
Core
109. The amount of current used
The more current, the stronger the electromagnet
The number of coils used on the core
The more coils, the stronger the electromagnet
Coils
110. Magnetic Force
Force on the wire is
perpendicular to the plane
containing the line of the wire
and the line of the magnetic
field. i.e. into the page
111. Force (F) on the wire is proportional to the current and the length (L)
of the wire in the magnetic field.
F∝ 𝑰𝑳
F= B *I * L
B is the magnetic field strength
B= F/ IL (B perpendicular to I)
Units of B are Newtons per meter per ampere
(SI unit) of magnetic field strength TESLA
NIKOLA TESLA (1856 – 1943) Croatia
1T = 1N.𝒎−𝟏
. 𝑨−𝟏
112. Electromagnetic Induction
A changing magnetic field in the vicinity of a wire or coil will induce
a voltage in the wire or coil.
FARADAY’S LAW OF MAGNETIC INDUCTION
Induced voltage is proportional to the rate of change of magnetic
flux through the coil.
Magnetic fluxɸ = 𝒎𝒂𝒈𝒏𝒆𝒕𝒊𝒄 𝒇𝒊𝒆𝒍𝒅 𝒔𝒕𝒓𝒆𝒏𝒈𝒕𝒉 𝒙 𝒂𝒓𝒆𝒂
ɸ = B.A
113. Moving scrap metal
Turn on the current to pick up scrap
Turn off the current to drop the scrap
114. Speakers
By varying the electric current through the wires around the
electromagnet, the speaker cone moves back and forth.
The resulting vibration of the speaker cone will create sound
waves, including that from voice and music.
115. Metal detectors
Electric current passes though a coil of wire wrapped around a
metal loop, creating the electromagnet. As the magnet is moved
over a metal object, the object creates interference in the
magnetic field. This interference is detected by the control box,
which produces an audible signal.
116. Electric Motors
An electric motor is a device which converts electricity to
mechanical energy.
An electromagnet turns inside of a permanent magnet. By
changing the direction of the current, the poles will keep
switching between N and S, and therefore cause the
electromagnet to continually rotate.
117. Electric motors are used in most
household appliances which convert
electricity into motion.
118. Electromagnetic levitation (mag-lev)
In electromagnetic levitation, a train or other vehicle is
supported and propelled by the repulsive forces of permanent
and electromagnets.
119. Strong permanent magnets on the bottom of the train are
repelled by the electromagnets in the track.
This supports the train, and by allowing the
electromagnetic current to travel, the train is in turn
pushed along.
120.
121. MEDICAL USES OF MAGNETIC FIELDS
Magnetic fields can penetrate tissue with
little or no adverse effects--- can be used
to probe the body.
NUCLEAR MAGNETIC RESONANCE NMR
MAGNETIC RESONANCE IMAGING MRI
DENTAL PROSTHESES RETENTION
122. MRI
NON-INVASIVE imaging technique that
discriminates between body tissues.
diagnostic tool for soft tissue- organs,
ligaments, the circulatory system, spinal
column, brain
uses superconducting magnet
Earth’s magnetic field = 0.5 x 𝟏𝟎−𝟒 𝒕𝒆𝒔𝒍𝒂
Fridge magnet= 𝟏𝟎−𝟑
𝒕𝒆𝒔𝒍𝒂
MRI Scanner magnet = 3 tesla
-6 x 𝟏𝟎𝟒
times the earth’s magnetic field
123. What is a galvanometer?
A galvanometer is an electromagnet that interacts with a permanent
magnet. The stronger the electric current passing through the
electromagnet, the more is interacts with the permanent magnet.
The greater the current passing through the wires, the stronger the
galvanometer interacts with the permanent magnet.
124. What are electric motors?
An electric motor is a device which changes electrical
energy into mechanical energy.
127. We have seen how electricity can produce a magnetic field,
but a magnetic field can also produce electricity! How?
What is electromagnetic induction?
Moving a loop of wire through a magnetic field produces an
electric current. This is electromagnetic induction.
A generator is used to convert mechanical energy into
electrical energy by electromagnetic induction.
